Resource Reservation Protocol (RSVP) is a protocol, i.e., a transport layer protocol as defined in RFC 2205 which may be found at http://www.rfc-editor.org/rfc/rfc2205.txt, designed to allow an application to reserve resources across a network for a given data flow. A data flow is typically constrained in scope to a 5-tuple identification that includes a source address, a destination address, a source port, a destination port, and a transport protocol.
Many applications transmit more than one distinct data flow. Such applications that transmit multiple distinct data flows may cause some data flows to reduce their transmission rates to lower rates than asked for within reservation set-up messages in order to effectively share network resources with other data flows. When multiple data flows associated with an application are each transmitted over different ports, each of the data flows independently reserves bandwidth using RSVP. If there is insufficient bandwidth available to meet all of the requests for bandwidth, even if it may be possible to reduce the rate of flow for any of the data flows, reducing the rate of a data flow which utilizes one port does not alleviate bandwidth issues for a data flow that utilizes a different port. For example, as bandwidth is not shared amongst data flows, when a data flow that uses a first port has its rate reduced, any bandwidth issues for data flows that utilize different ports is not alleviated. Thus, all of the multiple data flows are not able to be transmitted, as relying on RSVP to reduce bandwidth for a particular data flow associated with an application may not be sufficient to allow all distinct data flows associated with the application to be transmitted.